Fluoroquinolone antibiotics having the potential to interfere with fluorescence-based diagnosis.

Fluorescence, both intrinsic and exogenously induced, is being used for diagnosis of abnormal tissue. Excitation wavelengths used by these methods range from 320 to 450 nm. The presence of absorbing or fluorescing drugs is rarely taken into account by practitioners of fluorescence diagnosis and has the potential to yield false-positive or false-negative results. Our aim is to quantify this potential by (1) comparing the quantum yield of fluoroquinolone antibiotics to those of known tissue fluorophores and (2) taking into account drug concentrations in the tissue during treatment. Quantum yields are determined relative to a working standard of Rhodamine 6G in ethanol. The working standard was calibrated against a fluorescein standard. We concentrated our initial efforts on (1) the fluoroquinolone antibiotics, ciprofloxacin, norfloxacin and ofloxacin and (2) the intrinsic tissue fluorophores, NADH, FAD and protoporphyrin IX. When ciprofloxacin, norfloxacin and ofloxacin were excited at wavelengths 310-390 nm, emission occurred from 350 to 650 nm with quantum yields ranging from 0.03 to 0.3. Quantum yields for intrinsic fluorophores excited at their peak absorption wavelengths were 0.02 (NADH, 340 nm), 0.035 (FAD, 450 nm) and 0.087 (protoporphyrin IX, 408 nm). A review of the literature shows that these fluoroquinolones have a large volume of distribution and can be found in high concentrations in almost every organ during a treatment regimen. The product of the drug tissue concentration and quantum yield, which we term the fluorescence effective concentration, is such that it is likely these fluoroquinolones will interfere during fluorescence diagnosis techniques.

Evaluation of a fiberoptic-based system for measurement of optical properties in highly attenuating turbid media.

BACKGROUND: Accurate measurements of the optical properties of biological tissue in the ultraviolet A and short visible wavelengths are needed to achieve a quantitative understanding of novel optical diagnostic devices. Currently, there is minimal information on optical property measurement approaches that are appropriate for in vivo measurements in highly absorbing and scattering tissues. We describe a novel fiberoptic-based reflectance system for measurement of optical properties in highly attenuating turbid media and provide an extensive in vitro evaluation of its accuracy. The influence of collecting reflectance at the illumination fiber on estimation accuracy is also investigated. METHODS: A neural network algorithm and reflectance distributions from Monte Carlo simulations were used to generate predictive models based on the two geometries. Absolute measurements of diffuse reflectance were enabled through calibration of the reflectance system. Spatially-resolved reflectance distributions were measured in tissue phantoms at 405 nm for absorption coefficients (mu(a)) from 1 to 25 cm-1 and reduced scattering coefficients (mu'(s)) from 5 to 25 cm-1. These data and predictive models were used to estimate the optical properties of tissue-simulating phantoms. RESULTS: By comparing predicted and known optical properties, the average errors for mu(a) and mu'(s) were found to be 3.0% and 4.6%, respectively, for a linear probe approach. When bifurcated probe data was included and samples with mu(a) values less than 5 cm-1 were excluded, predictive errors for mu(a) and mu'(s) were further reduced to 1.8% and 3.5%. CONCLUSION: Improvements in system design have led to significant reductions in optical property estimation error. While the incorporation of a bifurcated illumination fiber shows promise for improving the accuracy of mu's estimates, further study of this approach is needed to elucidate the source of discrepancies between measurements and simulation results at low mu(a) values.

Reflectance-based determination of optical properties in highly attenuating tissue.

Accurate data on in vivo tissue optical properties in the ultraviolet A (UVA) to visible (VIS) range are needed to elucidate light propagation effects and to aid in identifying safe exposure limits for biomedical optical spectroscopy. We have performed a preliminary study toward the development of a diffuse reflectance system with maximum fiber separation distance of less than 2.5 mm. The ultimate objective is to perform endoscopic measurement of optical properties in the UVA to VIS. Optical property sets with uniformly and randomly distributed values were developed within the range of interest: absorption coefficients from 1 to 25 cm(-1) and reduced scattering coefficients from 5 to 25 cm(-1). Reflectance datasets were generated by direct measurement of Intralipid-dye tissue phantoms at lambda=675 nm and Monte Carlo simulation of light propagation. Multivariate calibration models were generated using feed-forward artificial neural network or partial least squares algorithms. Models were calibrated and evaluated using simulated or measured reflectance datasets. The most accurate models developed-those based on a neural network and uniform optical property intervals-were able to determine absorption and reduced scattering coefficients with root mean square errors of +/-2 and +/-3 cm(-1), respectively. Measurements of ex vivo bovine liver at 543 and 633 nm were within 5 to 30% of values reported in the literature. While our technique for determination of optical properties appears feasible and moderately accurate, enhanced accuracy may be achieved through modification of the experimental system and processing algorithms.

Selective detection of fluorophore layers in turbid media: the role of fiber-optic probe design.

Experimental verification of the ability to alter the sensitivity to fluorophore layers in turbid media by varying illumination-collection geometry is presented. Fiber-optic probes and two-layer, fluorophore-doped, turbid phantoms are used to elucidate the roles of spot size, illumination-collection fiber separation, and probe-sample spacing. Variations in single- and multiple-fiber probe design parameters produce significant changes in the relative sensitivity to sample layers in a manner that agrees with prior computational studies.